1. Field of the Invention
The present invention relates to a cryogenic system for radiation detector comprising:
a finger cooled to a low temperature and adapted for supporting and cooling said detector,
a wall surrounding said finger having, opposite said detector, a window transparent to the radiation to be detected
and in which the enclosure defined by said finger and said wall is closed and filled with at least a gas.
2. Description of the Prior Art
The present invention applies to all sorts of radiation detectors having to operate at very low temperatures, in particular infra red radiation detectors.
A cryogenic system of the above type is already known and described in patent FR-A-1 529 857. In this device, the gas filling the enclosure, as well as its pressure, are chosen so that its liquefaction temperature is smaller than that reached by the cooling finger.
Compared with conventional systems, in which the thermal insulation is provided by evacuating the enclosure defined by the finger and the wall, the present system has the main advantage of not requiring a fastidious pumping operation whenever the detector is to be changed.
To provide a certain thermal insulation, the wall defining the enclosure is a double wall under a sealed vacuum, which increases the cost of the apparatus and, despite this precaution, taking into account the fact that the thermal conductivity of the gas filling the enclosure is not zero, the time of self-supporting operation of the system, that is the time during which the temperature of the detector remains less than a certain value, for a given cooling time, is less than that of a conventional vacuum system of the same dimension.
The present invention overcomes these drawbacks.